This invention relates to auxiliary load supporting axles for wheeled vehicles, for example transit concrete mixers.
Transit concrete mixing trucks typically include a cab for the operator, and a rotatable drum behind the cab for containing and mixing the concrete ingredients. Such trucks further typically include steering wheels near the cab, and rear drive wheels often provided in a dual axle arrangement. For additional support, particularly in transit when the drum is substantially full, a mixing truck can have an auxiliary axle pivotally mounted between a raised position wherein it is carried by the truck, and a lowered or operating position wherein the auxiliary axle and its wheels share the truck's load with the steering and drive wheels, and ensure that the truck complies with state and federal gross axle weight regulations. Such an axle can be a "push" axle located ahead of the drive wheels, or a "tag" axle at the rear of the truck.
The prior art evidences various approaches for mounting auxiliary axles, not only to raise and lower such axle but permit it to adjust to uneven terrain and to follow the steering and drive wheels with minimal transverse skidding, particularly during turns. This latter feature is shown in U.S. Pat. No. 3,317,193 to Buelow et al granted May 2, 1967, in which a tag wheel assembly has a vertical shaft 70 which rotates in a vertical sleeve 68 attached to the chassis. U.S. Pat. No. 3,161,418 to Brennan et al granted Dec. 15, 1964 shows wheels with individual king pins 22 pivotally mounted to the vehicle frame. In U.S. Pat. No. 4,314,709 to Silbernagel granted Feb. 9, 1982, auxiliary wheels 51 are turned simultaneously by a tie rod 52, with vibrations damped by shock absorbers 53.
The Silbernagel Patent also shows leaf springs 40, which keep auxiliary arms 22 raised unless overcome by the force of air springs 27. U.S. Pat. No. 4,501,437 to Becker granted Feb. 26, 1985 discloses another scheme for raising and lowering a load transfer axle assembly, in which air springs 101 and 102 are used to lower the assembly, while a third air spring 120, using rods 132 and cables 134 attached to the assembly, can be extended to raise the assembly. Finally, U.S. Pat. No. 4,157,188 to Sims granted June 5, 1979 shows air bags 91 and 92 for lowering a tag axle 56, which is retracted upward by springs 90 when the air bags are not activated.
While the devices taught in these patents are satisfactory in many respects, there remains a need for a simple, low cost and reliable mounting for an auxiliary axle to conveniently move it into and out of its operating position, and to ensure tracking during turns and adjustment to uneven terrain.
It is therefore an object of the present invention to provide a low cost, reliable means for carrying an auxiliary axle on a wheeled vehicle.
Another object of the invention is to provide a mounting enclosure for an auxiliary axle that permits pivoting of the auxiliary axle into and out of an operating position about a transverse and horizontal pitch axis, and further allows limited rotation of the axle about a longitudinal roll axis for adjustment to uneven terrain.
Yet another object of the invention is to mount an auxiliary axle to provide limited rotation about a vertical yaw axis in order to allow the wheels of the auxiliary axle to track during turns, without individual castor mounting of the wheels.
Another object of the invention is to provide an auxiliary axle mounting that continually tends to center the axle relative to a vehicle chassis.